Iranian media has reported that Turkmen naval vessels fired on an Iranian fishing boat killing one of the fishermen and sinking the boat.
The Tehran Times reported on February 1 that the incident happened in December when Turkmenistan's navy "shot a number of fishermen in the Caspian Sea without prior warning."
IRNA reported the surviving Iranian fishermen were taken into custody by Turkmen forces and as yet "there is no exact information about the fate of [the] crew."
IRNA called the attack "a move beyond diplomatic norms and contrary to international law," while the Iran Daily said it was "against international conventions."
Such incidents are rare between Iran and Turkmenistan but the status of the Caspian Sea and its maritime borders are still not settled between the countries surrounding it -- Azerbaijan, Russia, Kazakhstan, Turkmenistan, and Iran.
The Caspian Sea has also become a transit route for narcotics coming from Afghanistan and all the Caspian littoral states have been building their naval and maritime security forces.